We have previous data from frogs suggesting that one of the mechanisms basic to olfactory discrimination may be the differential sorption of molecules of different odorants across the mucosa. We will pursue this line of study in frogs and other species by radioisotopically defining exactly how the molecules are distributed to the receptors, what parameters affect these distributions, and how the distributions may make an impact upon the processing of olfactory information by the central nervous system. (1) We are developing a hot-wire anemometer to profile air movements into and out of the olfactory sac of the bullfrog, we will soon develop an odorant delivery system to faithfully reproduce this normal behavior for sampling odorants. (2) Using the anemometer profile we will present animals with tritium-labelled odorants and using liquid scintillation counting to measure the resultant radioactivity in different mucosal regions, we will map exactly how the molecules of different odorants are distributed across the length and breadth of the olfactory receptor sheet. The stability of these distribution patterns will be tested as a function of stimulus duration, concentration and flow rate. (3) Using autoradiographs, we will follow the distribution of the molecules vertically through the depth of the mucosa, noting particularly any differential filtering of different chemicals. (4) Autoradiographic and liquid scintillation counting techniques will be used to determine the in vivo interactions of the mechanisms (desorption in air, mucus flow, blood uptake, and absorption by sustentacular and receptor cells) which remove odorant molecules from the olfactory mucosa. (5) By recording from single mitral cells in the olfactory bulb previously shown by electrical stimulation to receive their input from particular regions of the olfactory receptor sheet, we will determine whether the differential molecular distributions established across the mucosa are topographically represented by a group of mitral cells in the olfactory bulb. (6) Using liquid scintillation techniques, the access and degrees of odorant molecules to the inferior nasal cavity and vomeronasal gland will be studied. (7) Labelled compounds will be used to study the possibility that following olfactory receptor interaction odorant molecules may be changed chemically.